Caption: Light micrograph of the unicellular cyanobacteria (blue-green algae), Chroococcus, seen in its four- celled growth stage. Chroococcus cells are typically surrounded by a colloidal sheath (transparent, seen here); after cell division many cells may cohere, due to this sheath, to form colonies. Cyanobacteria are primitive algae and regarded closer to bacteria. They are prokaryotic organisms with no membrane-bound nucleus, & their chloroplasts are not restricted by a membrane but lie free in the cell. Chroococcus is found in aquatic environments, including waterfalls and peat soils. Magnification: x30 at 35mm size.